1. Technical Field
The present disclosure relates to a method of preparing an anti-adhesion barrier from hyaluronic acid, to the anti-adhesion barrier formed thereby, and to methods of using the anti-adhesion barrier.
2. Background of the Related Art
Hyaluronic acid is a viscous mucopolysaccharide found in animal and human tissues such as the umbilical cord, vitreous humor, synovial fluid, blood vessel walls and other connective tissues. The polysaccharide consists of repeating disaccharide units made of alternating D-glucuronic acid and N-acetyl-D-glucosamine residues, and possesses a molecular weight ranging from about 40,000 to 8,000,000 depending on the source and methods of extraction. Hyaluronic acid is found in between cells complexed with proteins, and forms a jelly due to its ability to retain water. It plays an important role in various biological processes, such as cell migration, lubrication, moistening of tissues, and maintenance of cell morphology (Meyers, Physiol. Rev., 27: 335, 1947).
Its natural occurrence in the body and its ability to retain water have lead to the development and use of hyaluronic acid for various therapeutic applications, e.g., the treatment of arthritis, the use of hyaluronic acid as a vitreous humor substitute, the prevention or inhibition of adhesions following surgery, and the protection of wounds during healing. However, upon administration to an individual, hyaluronic acid undergoes enzymatic degradation by various enzymes, e.g., hyaluronidase, glucoronidase, and glucosidase, or non-enzymatic degradation (Pigman et al., Arthritis Rheumatism 4: 240, 1961), and thus does not maintain its original viscosity or desired residence time in vivo.
One successful approach to delay degradation of hyaluronic acid when administered to the body, and thus preserve its original viscosity and residence time in vivo, has been to modify hyaluronic acid with a crosslinking agent. Various crosslinking agents and methods have been utilized to crosslink hyaluronic acid for use in various therapeutic applications. For example, U.S. Pat. No. 4,716,224 describes the crosslinking of hyaluronic acid with the use of poly-functional epoxy compounds wherein the hyaluronic acid is dissolved and reacted with the epoxy compounds in an alkaline medium. The crosslinked hyaluronic acid is described as useful in the treatment of arthritis and as an ingredient of cosmetics.
U.S. Pat. No. 4,886,787 describes crosslinking hyaluronic acid with di or polyfunctional epoxides wherein the hyaluronic acid is dissolved and reacted with the epoxides in an acidic solution, in the presence of an acidic catalyst. The crosslinked hyaluronic acid is proposed to be useful in the treatment of arthritis, as a drug delivery vehicle, to reduce post-operative adhesions, to promote wound healing, and as a component of cosmetics.
U.S. Pat. Nos. 4,582,865, 4,605,691 and 4,636,524 describe the reaction of divinyl sulfone as crosslinking agent with hyaluronic acid in an aqueous alkaline solution. The crosslinked hyaluronic acid is described as being useful in cosmetic formulations and drug delivery systems.
U.S. Pat. No. 5,356,883 describes crosslinking hyaluronic acid with the crosslinking agent carbodiimides to produce hydrogels which are purportedly useful as biocompatible gels, films or sponges.
U.S. Pat. No. 4,957,744 describes crosslinking hyaluronic acid with polyhydric alcohols to produce crosslinked hyaluronic acid esters, which are described as useful for treatment of arthritis, and as components of cosmetics. The crosslinking reaction is effected by dissolving and reacting hyaluronic acid with a crosslinking agent in polar and non-polar solvents.
U.S. Pat. No. 5,690,961 describes crosslinking hyaluronic acid with di- or polyanhydrides in a polar, aprotic solvent. The anhydride-crosslinked hyaluronic acid is proposed to be useful in the treatment of arthritis, as a drug delivery vehicle, to reduce the formation of post-operative adhesions, to promote wound healing and as an ingredient in cosmetics.
U.S. Pat. No. 5,532,221 describes the production of ionically-crosslinked hyaluronic acid, wherein an aqueous solution of hyaluronic acid is contacted with an aqueous polycation solution. The ionically-crosslinked hyaluronic acid is described as useful in preventing post-operative adhesions.
In the literature described above, regardless of the particular crosslinking agent used, the crosslinking of hyaluronic acid is carried out in a homogenous solution state, wherein hyaluronic acid is dissolved and reacted with the crosslinking agent in a solution. Since the solubility of hyaluronic acid in aqueous solution is very low, the reactions carried out in such homogenous solutions are not efficient. Accordingly, recovery of the reaction product can be difficult.
A method of forming an anti-adhesion barrier is provided which comprises freeze-drying a solution including hyaluronic acid to form a foam, reacting the foam with a crosslinking agent to form a crosslinked foam and mixing the crosslinked foam with an aqueous solution containing hyaluronic acid to form the anti-adhesion barrier.
In another aspect, an anti-adhesion barrier is provided which is a gel produced by combining a freeze-dried crosslinked hyaluronic acid foam and an aqueous solution including hyaluronic acid.
In yet another aspect, a two-part kit is provided which comprises a first part including freeze-dried crosslinked hyaluronic acid foam, and a second part including a solution including hyaluronic acid.
As stated previously, prior art methods for preparing crosslinked hyaluronic acid, in general, involve a crosslinking step which is performed in a homogenous solution state, i.e., hyaluronic acid is dissolved and reacted with a crosslinking agent in a solution. In contrast, the present method of preparing an anti-adhesion barrier involves a unique solid-state crosslinking reaction wherein hyaluronic acid is prepared as a solid, i.e., freeze-dried foam, which is then reacted with a neat liquid crosslinking agent to yield a crosslinked hyaluronic acid foam. This method eliminates the concern of low solubility of hyaluronic acid in various solvents. Also, because the crosslinking agents only react with those functional groups accessible on surfaces, the use of a freeze-dried hyaluronic acid foam provides a relatively large surface area containing sites at which crosslinking can occur.
The production of crosslinked hyaluronic acid foam in accordance with the method of the present invention results in a near-quantitative recovery of crosslinked hyaluronic acid foam. The excess crosslinking agents and any reaction by-products can be easily removed by simple washing. In contrast, recovery of crosslinked hyaluronic acid produced by the methods of the prior art wherein crosslinking is conducted in homogenous solution state is less efficient and removal of excess crosslinking agents and reaction by-products is more time consuming.